It is increasingly a requirement of bicycles that they should be reliable, meet the requirements of traffic safety and be able to be quickly set up and taken down. Furthermore, they should have small dimensions and small spatial requirements so that they can be stored anywhere, thus for example in an apartment, possible under a piece of furniture or a bed, in the hall, at a desk, beside or under a work-bench in the place of employment without causing injuries to passers-by with their protruding parts, e.g. pedals etc. It should be possible to carry such a portable bicycle by hand, folded-up, in a public vehicle without hindering or injuring anyone or causing an accident; the bicycle must be light so that carrying it will not require great physcial effort; and placing the bicycle in operation should not require special skill.
These requirements are not fully met with any of the bicycles produced so far, as regards their form, weight and design.
The present exterior form and design of the bicycles go back nearly a century, utilizing a frame welded together of thin-walled steel tubes, a fork, a rear wheel driven by pedals through a chain drive and a front freely-rotating wheel which can be steered by a handlebar, a saddle, a brake and auxiliary units.
Depending on the shape of the frame these bicycles may be men's bicycles, where the saddle and the handlebar are connected horizontaly with a tube, or lady's bicycles where no similar horizontal tube is used, or bicycles to be folded up, for both men and women and which, after usage, in order to take up less room can generally be dismantled at one point of the frame or folded up at a hinge by turning one wheel on top of the other. Among these bicylces there are those which have been made lightweight for racing but have geometries and dimensions corresponding to those of ordinary bicycles. A common characteristic of these bicycles is that they require much room, they are heavy, storage is a problem, and they cannot be carried in the form of a bag.
Manufacturers of the known bicycles in circulation and use, strive to eliminate the above-described drawbacks with various measures, including smaller wheel diameters, making the frame and the fork structure of light-metal tube, facilitating the dismounting of the wheels and enabling the turning inward of the pedals. Bicycles are also known, which can be fully dismantled and placed in a rucksack or in a case made especially for carrying or storing.
These solutions make the bicycles suitable for many purposes but do not enable people living in multi-family housing to store them in an appropriate way, e.g. in their apartments, or permit children requiring much exercise to take them along or disassemble and assemble them in a short period, then put them into operation reliably, because the bicycles known so far are so heavy that they cannot be carried up stairs, there may be no store-rooms for bicycles or, if there are, these may be too small. Besides, bicycles may not be stored safely in them. They cannot be taken for excursions in a public vehicle and require much room in other transport means and create problems with transportation; they cannot be taken into offices, etc. because of their great spatial requirements. Hence their use is restricted in most cases.